9 Tube Stereo Amplifier
20 Watts per channel Maximum
Want big tube room filling sound without the trouble or expense of big tube equipment? Look no further! This 9 tube amp is simple to operate, powerful, and uses only 3 types of tubes. This amp features a 6BQ5 push-pull output for each channel, and two quiet, reliable 6EU7 tubes in each channel as well. A 5U4-G keeps plenty of power flowing. You have complete control with powerful bass and treble tone controls, and a balance control compensates for any speaker/room or source audio deficiencies.
Schematic:
The Magnavox-style output section uses a paraphase inverter and a minimum of circuit components. An inverse feedback loop minimizes distortion to give you clean, room filling tube sound. This is a powerful amplifier, if you live in a dorm room or small apartment, you may have difficulty, as this amplifier does not like to play at low volume levels.
Parts List
|
Control Resistors |
|
|
|
Resistor ID |
Value (ohms) |
Function, Notes |
|
R1A & B |
Dual-section 500K audio taper 1/2W |
Volume Control |
|
R2A & B |
Dual-section 1M linear taper 1/2W |
Bass Control |
|
R3A & B |
Dual-section 1M linear taper 1/2W |
Treble Control |
|
R4 |
750 linear taper 1W |
Balance Control |
|
Fixed Resistors |
|
|
|
R5, R23 |
2.2K 1/2W |
Input amp cathode |
|
R6, R24 |
220K 1/2W |
Input plate load |
|
R7, R25 |
10K 1/2W |
Bass tone comp |
|
R8, R26 |
100K 1/2W |
Bass tone comp |
|
R9, R27 |
100K 1/2W |
Audio coupling |
|
R10, R28 |
2.7K 1/2W |
Tone amp cathode |
|
R11, R29 |
82K 1/2W |
Tone amp plate load |
|
R12. R30 |
470K 1/2W |
Grid load |
|
R13, R31 |
47K 1/2W |
Grid input |
|
R14, R32 |
5.6K 1/2W |
Inverter cathode |
|
R15, R33 |
2.2K 1/2W |
Driver cathode |
|
R16, R34 |
220K 1/2W |
Plate load |
|
R17, R35 |
220K 1/2W |
Plate load |
|
R18, R36 |
220K 1/2W |
Output grid |
|
R19, R37 |
39K 1/2W |
Inverter grid |
|
R20, R38 |
470K 1/2W |
Output grid |
|
R21, R39 |
220K 1/2W |
Monitor isolation |
|
R22, R40 |
3.9K 1/2W |
Feedback coupling |
|
Power Resistors |
|
|
|
R41 |
100 10W wire wound |
Output cathodes |
|
R42 |
10K 5W wire wound |
Voltage divider |
|
R43 |
33K 2W metal oxide |
Voltage Divider |
|
R44 |
750 5W wire wound potentiometer |
Hum adjust |
|
Fixed Capacitors |
|
|
|
Capacitor ID |
Value |
Function, Notes |
|
C1, C10 |
0.047mF 630V |
Audio coupling |
|
C2, C11 |
0.002mF 630V |
Bass tone comp |
|
C3, C12 |
0.02mF 630V |
Bass tone comp |
|
C4, C13 |
0.0002mF 630V |
Treble tone comp |
|
C5, C14 |
0.002mF 630V |
Treble tone comp |
|
C6, C15 |
0.047mF 630V |
Audio coupling |
|
C7, C16 |
100mmf 630V |
B+ decoupling/snubber |
|
C8, C17 |
0.0047mF 630V |
Audio coupling |
|
C9, C18 |
0.047mF 630V |
Audio coupling |
|
C19 |
0.01mF 1400V |
Line bypass |
|
Electrolytic Capacitors |
|
|
|
C20 |
22mF 25V |
Cathode bypass |
|
C21 |
47mF 450V |
Filter |
|
C22 |
33mF 450V |
Filter |
|
C23 |
10mF 450V |
Filter |
|
C24 |
33mF 450V |
Filter |
|
Choke ID |
Inductance (henries @ 1000 cps) |
Current, notes |
|
L1 |
1 henry |
130 ma @ 330 volts, U-bracket |
|
Power Transformer, T1 |
|||
|
Primary |
Sec. 1 |
Sec. 2 |
Sec.3 |
|
117V AC 60cps .92A |
600V CT 130ma |
5 volts 3 amps |
6.3 volts 4 amps |
|
Output Transformers T2, T3 |
|
|
Primary Impedance |
Secondary Impedance |
|
8000 ohms,CT @ 400 cps |
Matched to speakers, with a tap @ 4 ohms for feedback. |
|
Miscellaneous Parts |
|
|
|
Part ID |
Description |
Function, Notes |
|
SW1A & B |
2-pole, 6-throw make-before break switch |
Audio Selector Switch |
|
SW2 |
Single-pole, single-throw switch, 5A rated |
Power Switch |
|
V1 |
6EU7 |
Input amp-tone amp left channel |
|
V2 |
6EU7 |
Driver-phase inverter left channel |
|
V3 |
6EU7 |
Input amp-tone amp right channel |
|
V4 |
6EU7 |
Driver-phase inverter right channel |
|
V5 |
6BQ5 |
Output left channel |
|
V6 |
6BQ5 |
Output left channel |
|
V7 |
6BQ5 |
Output right channel |
|
V8 |
6BQ5 |
Output right channel |
|
V9 |
5U5-G |
Current rectifier |
Created 11-21-09
Back to the Radio and Electronic Page.